英文:
How to properly implement JOIN/ UNION ALL in a query when selecting columns from all tables in a database?
问题
I'm trying to select all tables with their max value of TimeLoaded. TimeLoaded is a timestamp. So my output should be similar to this:
我尝试选择所有表格及其TimeLoaded的最大值。TimeLoaded是一个时间戳。因此，我的输出应该类似于这样：
英文:
Assume I have many tables in a database.
I'm trying to select all tables with their max value of TimeLoaded. TimeLoaded is a timestamp. So my output should be similar to this:
Since I am trying to select every table in the database while retrieving the max value of TimeLoaded, I am unsure how to implement JOIN and UNION ALL as there may be a database with 20 or more tables.
答案1
得分: 1
SELECT TOP (1) MAX(TimeLoaded) as TimeLoaded, 'Arrival' AS Tables FROM [your_db_name].[dbo].[Arrival]
Union
SELECT TOP (1) MAX(TimeLoaded) as TimeLoaded, 'Duration' AS Tables FROM [your_db_name].[dbo].[Duration]
Union
SELECT TOP (1) MAX(TimeLoaded) as TimeLoaded, 'Departure' AS Tables FROM [your_db_name].[dbo].[Departure]
Union
SELECT TOP (1) MAX(TimeLoaded) as TimeLoaded, 'Alert' AS Tables FROM [your_db_name].[dbo].[Alert]
英文:
I do not know how to select table name, but maybe you can try this:
SELECT TOP (1) MAX(TimeLoaded) as TimeLoaded, 'Arrival' AS Tables FROM [your_db_name].[dbo].[Arrival]
Union
SELECT TOP (1) MAX(TimeLoaded) as TimeLoaded, 'Duration' AS Tables FROM [your_db_name].[dbo].[Duration]
Union
SELECT TOP (1) MAX(TimeLoaded) as TimeLoaded, 'Departure' AS Tables FROM [your_db_name].[dbo].[Departure]
Union
SELECT TOP (1) MAX(TimeLoaded) as TimeLoaded, 'Alert' AS Tables FROM [your_db_name].[dbo].[Alert]
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